A known internal gear pump includes a housing having a pump chamber, an inner rotor having external teeth on its outer end and arranged in the pump chamber, an outer rotor, whose rotational axis differs from the inner rotor, having internal teeth on its inner end and arranged in the pump chamber, a suction port that is in communication with the pump chamber and supplies a fluid thereto, a suction path in communication with the suction port, a discharge port that is in communication with the pump chamber and discharges the fluid therefrom, and a discharge path in communication with the discharge port, wherein a groove for generating a discharge pressure in a direction such as to negate a force applied to the outer rotor is formed at an inner wall at a location close to the discharge port (see for example the Patent Document 1).
Another known internal gear pump includes a housing having a pump chamber, an inner rotor having external teeth on its outer end and arranged in the pump chamber, an outer rotor, whose rotational axis differs from the inner rotor, having internal teeth on its inner end and arranged in the pump chamber, a suction port that is in communication with the pump chamber and supplies a fluid thereto, a suction path in communication with the suction port, a discharge port that is in communication with the pump chamber and discharges the fluid therefrom, and a discharge path in communication with the discharge port, wherein a groove for supplying the fluid to an outer circumference of the outer rotor is provided at an inner wall of the pump chamber at a location extending along the suction port (see for example the Patent Document 2).